Maize floral regulator protein INDETERMINATE1 is localized to developing leaves and is not altered by light or the sink/source transition.

The INDETERMINATE1 gene, ID1, encodes a putative transcription factor that plays an important role in regulating the transition to flowering in maize. Mutant id1 plants have a prolonged vegetative growth phase and fail to make normal flowers. The ID1 gene, which encodes a nuclear-localized zinc finger protein, is expressed exclusively in immature leaves, suggesting that ID1 regulates a leaf-derived floral inductive signal. It is shown by western analysis with anti-ID1-specific antibody that ID1 co-localizes with ID1 mRNA in developing, immature leaves and, similarly, is absent in mature, photosynthetically active leaf blades, as well as the shoot apical meristem. Immunolocalization with anti-ID1 antibody shows that ID1 protein is detected in the nuclei of all cell types in immature leaves. Examination of plants grown in different day/night cycles revealed that ID1 gene expression and protein levels are largely unaffected by variations in light and dark, and that mRNA and protein levels do not follow a circadian pattern. The absence of ID1 expression in greening leaf tips coincides with the sink-to-source transition of developing leaves. It was found that ID1 levels are down-regulated in mature albino leaves similarly as in normal green leaves, suggesting that ID1 activity is controlled developmentally and is not affected by the sink/source status of the leaf or the inability of a mature leaf to engage in photosynthesis. The finding that ID1 expression is developmentally regulated and is unperturbed by external stimuli such as photoperiod supports the supposition that ID1 acts through the autonomous floral inductive pathway in maize.